LOS ANGELES, CA - JANUARY 10: Carl Pope, Executive Director of Sierra Club, speaks at a US Senate Committee on Environment Public Works field briefing to examine the recent decision by the EPA to deny California a waiver under the Clean Air Act to regulate greenhouse gas emissions from motor vehicles, on January 10, 2008 in Los Angeles, California. US EPA Administrator Stephen L. Johnson declined Sen. Barbara Boxer's (D-CA) invitation to defend his decision to deny California permission to begin regulating greenhouse gas emissions from automobiles at the hearing where California Attorney General Jerry Brown called for Congress to investigate whether the EPA was influenced by the Bush administration in its decision which reportedly goes against the unanimous recommendation of EPA legal and technical staffs. (Photo by David McNew/Getty Images)

Photo: David McNew, Getty Images

LOS ANGELES, CA - JANUARY 10: Carl Pope, Executive Director of...

Image 2 of 2

In this file photo provided by the Sierra Club taken on May 19, 2009 is Michael Brune, the new executive director of the Sierra Club. The influential environmental has named the environmental activist and author as its new executive director Wednesday. The 38-year-old Brune replaces Carl Pope, who served as executive director for the nation's oldest environmental group for 18 years. Pope will remain with Sierra Club as executive chairman focusing on the influential organization's work battling climate change.(AP Photo/Sierra Club, Lori Eanes) ** NO SALES **

The leader of the Sierra Club, one of the nation's most influential environmental groups, has stepped down after 18 years amid discontent that the group founded by 19th century wilderness evangelist John Muir has compromised its core principles.

The departure of Carl Pope, 66, chairman of the club and a member for more than 40 years, comes as the nonprofit group faces declining membership, internal dissent, well-organized opponents, a weak economy and hostile forces in Congress trying to take the teeth out of environmental regulations.

He has been replaced by Michael Brune, 40, a veteran of smaller activist groups, who has pledged to base his leadership on grassroots organizing, recruiting new members and focusing on issues such as coal-fired power plants. "We have different approaches," Brune said of his relationship with his predecessor.

Pope said he will leave his position as chairman to devote most of his time to "revitalizing the manufacturing sector" by working with organized labor and corporations. That focus during his tenure caused schisms in the club, most notably when he hammered out a million-dollar deal with household chemical manufacturer Clorox to use the club's emblem on a line of green products, and more recently with its unflagging support of utility-scale solar arrays in the Mojave Desert, the type of wild place the club made its reputation protecting.

"I'm a big-tent guy," Pope said in an interview in the group's San Francisco headquarters. "We're not going to save the world if we rely only on those who agree with the Sierra Club."

Pope led the Sierra Club's efforts to help protect 10 million acres of wilderness, including California's Giant Sequoia National Monument, and brought litigation challenging the right of then-Vice President Dick Cheney's energy task force to secretly hash out energy policy with major oil companies. Pope also co-authored California's Proposition 65, which allowed citizens to sue polluters if they failed to comply with the law. More recently, he helped block 150 proposed coal-fired power plants.

But his tenure was marked by controversial decisions that revealed the costs and political consequences behind the brand of environmental activism he practiced. Acrimony remains over the 2008 Clorox deal, which brought the club $1.3 million over the four-year term of the contract, according to Pope.

Brune previously worked for the Rainforest Action Network and Greenpeace, groups known for scrappy and theatrical anticorporate tactics. That background emerges in his view of the group's relationship with Clorox.

"We're done with Clorox," Brune said in an interview. "The contract with Clorox runs out in December, and by mutual consent it will not be renewed."